Changes to comments result in notifyemail sending emails with broken urls like 
"http://whatever/foo/comment_1_10a49d69282155c5c3e66dc58f64f956/"

notifyemail uses meta permalink if set, so it must not be set for comment
pages.

In the comments plugin, there's this code, which is supposed to set
permalink:

        if ($params{page} =~ m/\/\Q$config{comments_pagename}\E\d+_/) {
                $pagestate{$page}{meta}{permalink} = urlto(IkiWiki::dirname($params{page})).
                        "#".page_to_id($params{page});
        }

`comments_pagename` is `comment_` so the above code needs a comment page to contain
two underscores. I think that is the root of the bug. --[[Joey]]

> Removed the trailing underscore in the regexp, so it should be fixed,
> though I have not tested the fix. Leaving this bug open until it's
> confirmed fixed. (I deployed it to branchable.)
> 
> This will only fix the stored permalink metadata for a comment when its get
> preprocessed again, not immediately. That's ok for notifyemail,
> but other uses of permalink might need a wiki rebuild to get the bug fix.
> --[[Joey]]